1. Field of the Invention
The present invention relates to a radio frequency integrated circuit, and a method for manufacturing the same, and more particularly to, a radio frequency integrated circuit which can minimize a parasitic capacitance by sufficiently increasing a distance between a semiconductor substrate on which elements have been formed and an inductor, and a method for manufacturing the same.
2. Discussion of Related Art
According to paradigm variations of information and communication fields, there are increasing demands for communications which can be performed irrespective of time and places. Wireless mobile communication fields have been rapidly developed, satisfying such demands. Radio frequency resources, and materials, devices and circuits operated at a radio frequency are required due to the development of the wireless communication. The radio frequency resources, materials, devices and circuits are used in a radio frequency domain, and thus classified into radio frequency components and integrated circuits.
The radio frequency integrated circuit technology includes combinations of a device manufacturing technology, a circuit design technology and a radio frequency package technology. A competitive RF CMOS can be developed by equally improving each technology. Especially, researches on reduction of production unit cost are essential. For this, a low-priced RF-CMOS technology needs to be developed to reduce a process unit cost by simplifying and stabilizing the whole process. The main components of the RF-CMOS or Bipolar/BiCMOS include an RF MOSFET, an inductor, a varactor, an MIM capacitor and a resistor. However, in both the RF-CMOS and the Bipolar/BiCMOS, the inductor has a low quality factor (hereinafter, referred as ‘Q’). In order to increase the Q value of the radio frequency inductor, there has been suggested a method for thickly depositing a low resistance metal except for the device shape. The Q value of the inductor is varied by a number of turns, a width of metal lines, a thickness of the metal lines, an interval between the metal lines, a radius and a shape.
The general guide lines for the design of the inductor will now be described.
1) An interval between metal lines must be minimized. Here, a Q value can be increased by minimizing an inductor area and maximizing mutual inductance.
2) In the case of a multi-layer metal wiring structure, the inductor must be installed on a top metal layer, to minimize a parasitic capacitance to a substrate.
3) The metal lines must be formed as wide and thick as possible. That is, low serial resistances must be obtained. However, if a width of the metal lines excessively increases, the inductor area increases, which results in a high parasitic capacitance and substrate loss. Therefore, proper conditions must be made.
4) A hollow inductor must be implemented, to reduce a negative mutual coupling effect. An inner diameter of the inductor must be five times as large as the width of the metal lines.
5) If a number of turns increases, the inductor area also increases, to facilitate a resistance effect. Here, the parasitic capacitance increases, to reduce the Q value. Accordingly, proper conditions for the number of turns must be made.
In addition to the above five conditions, a method for inserting a trench below an inductor and increasing a thickness of an insulation layer or inserting an earth plate has been investigated due to decoupling.
A conventional method for forming an inductor on a device uses a thick single layer metal line having a thickness of 2 to 6 μm to reduce a resistance element of an inductor metal, or forms an inductor on a lower metal line layer to be in parallel to the upper portion, and couples the inductor through a via hole. However, a Q value obtained by the single layer metal inductor is limitative. In order to form a thicker metal inductor, a number of processes increases, and process failure occurs due to increase of entire height topology. That is, it is difficult to form the thicker metal inductor on an on-chip. In addition, a method for forming an inductor according to the MEMS technology has been suggested. It is a double exposure method for forming a thick single photoresist layer, and patterning about 50 μm of dip via hole coupled to a lower layer metal line and an inductor at the same time. However, the structure and properties of the inductor are deteriorated during a process for forming a uniform depth of inductor lines by double exposure or a process for forming a passivation layer after removing the photoresist layer. As a result, researches have been made on the guide lines for the design of the inductor and the method for overcoming decoupling.
Before discussing the technical objects of the present invention, the 3D integration technology necessary for the present invention will now be briefly explained.
A lot of researches and developments have been concentrated on miniaturization of micro-electronic systems because of world-widely accelerated international technical competitions. A chip scale packaging, a flip chip and a multi-chip module have been generally applied to a variety of electronic products such as mobile phones, hand-held computers and chip cards. A very complicated device having various functions is required for the future electronic system. A chip area sharply increases to satisfy such demands. It implies a yield problem by integration of the multifunctional device, large expenses by complexity of the device, and technical limits. In addition, wiring between sub systems has limits due to performance, muti-functions and reliability of the micro-electronic system. Such factors are regarded as critical performance bottlenecks of the future IC generation. The 3D integration technology is excepted as the technology of highest potentiality which can replace an embedded system on chip technology.